This invention relates to electronic sensors, and more specifically to a passive infrared movement detector having a reflecting device which directs the radiation from a plurality of fields of vision to an infrared detector arrangement and for this purpose consists of a plurality of individual reflectors.
A passive infrared movement detector is known from German Offenlegungsschrift No. 28 55 322. The reflecting surface of the reflector described therein is composed of a plurality of facets produced at the reflector. Movement detectors having such a reflector have essential disadvantages which are as follows: For each required range of action of the movement detector a reflector adapted thereto must be used, since the range of action of the movement detector is determined by the dimensions of the facets and, therefore, is invariable. Because the reflecting surface of the reflector is made in one piece, it is necessary, in the case when after the installation of the apparatus a source of errors is present in one of the coverages, to change the position of the whole apparatus in order to eliminate this source of errors. Thereby, it cannot be excluded that after the adjustment of the apparatus has been carried out, sources of errors become noticeable in other coverages which can only be eliminated by a further adjustment of the apparatus. Furthermore, an optimum surveillance becomes doubtful by the fact that by an adjustment of the movement detector by means of one facet of the reflector all other facets are compulsorily also adjusted. Finally, due to the plurality of facets to be produced, the production of the reflecting surface of the reflector is difficult and thus expensive.